In general, a tire-vulcanizing mold includes a pair of side plates for forming a side wall portion of a pneumatic tire, a pair of bead rings for forming a bead portion, and a sector mold for integrally forming a tread portion and both shoulder portions. The sector mold is separated into a plurality of sectors, and is annularly disposed around the tread portion of an unvulcanized pneumatic tire.
There are formed, on a tread forming surface of each of the sectors, for example, a main-groove forming bone for forming a main groove extending in a circumferential direction of a tire; a lug-groove forming bone for forming a lug groove extending in a width direction of the tire at the shoulder portion; a slant-groove forming bone for forming aslant groove slanted with respect to the circumferential direction of the tire at the shoulder portion and a center portion; and the like. Patterns of these groove forming bones on the sectors are formed through carving processing independently of the sectors, and are attached to each of the sectors as pattern blocks subjected to carving processing.
Incidentally, conventionally, patterns for forming the lug groove are mainly used as patterns of the pattern block. However, in recent years, in response to the requirements for tire performance, there has been an increasing tendency to include a narrow-groove forming bone.
Conventionally, carving processing on the pattern block is performed in a state where an entire periphery of the pattern block is fixed to a jig for pattern carving (hereinafter, simply referred to as a jig) through welding so as not to be misaligned. Therefore, in the case where the narrow-groove forming bone is fixed through welding, the entire periphery thereof has to be fixed through welding by setting a welding margin with which fixation strength for the narrow-groove forming bone can be ensured.
However, when the entire periphery of the pattern block is fixed to the jig through welding, there exists a problem in which a considerable number of processes become necessary in order to detach the pattern block from the jig. In addition, distortion is also likely to occur in the pattern block due to heat generated by welding fixation. In particular, in the case where the narrow-groove forming bone for the tire is formed, chattering or welding distortion generated during processing easily leads to reducing accuracy of processing. Furthermore, when chattering or welding distortion is generated during processing of the pattern block, it becomes necessary to correct warpage or bending at the time of attaching the pattern block to the sector after the processing.
Moreover, conventionally, when the pattern block is attached to the sector, a position of the pattern block is temporarily fixed by a bolt, and attachment positioning is performed while fine adjustment is being performed along a marking line drawn in advance on the sector. However, the positioning accuracy in the circumferential direction by using marking is not so good.
In addition, after a back body surface of the pattern block is machine-processed in accordance with a shape of a tread (sector face) of the sector, the pattern block is attached to the sector. Recently, an accuracy of machine processing of the back body surface of the pattern block is enhanced, therefore, an accuracy capable of being attached to the sector face without performing further machine-processing can be obtained. However, even if machine processing is performed with high accuracy, it is difficult to maintain the accuracy of machine processing, due to distortion or warpage or the like generated during the carving processing of the pattern block after the machine processing. Therefore, attachment is performed while a lapping operation is being performed between the back body surface of the pattern block and the sector face, but attachment of the pattern block to the sector is complicated and requires manual work. Furthermore, as to the lapping operation, since it is difficult to apply lapping to an entire surface, a clearance part is provided on a part of the back body surface, with the result that the lapping operation is performed so as to reduce a range (area) of lapping with respect to the tread of the sector. However, despite that, the complicated procedures are not sufficiently eliminated.
In contrast to this, for example, Patent Literature 1 describes a method of manufacturing a pattern block made of a steel plate in order to prevent generation of distortion in the case of welding the pattern block to a holder.
In this method, the steel plate is subjected to fusion cutting and then to rough machining. Subsequently, a clearance part is formed on a back surface of the holder (sector), the pattern block is formed, and the pattern block is welded to the holder. With this method, the distortion due to welding is less likely to be generated as compared with a case where the pattern block is formed through casting. However, in the first place, formation of the pattern block through casting is not an object of the method.
Patent Literature 2 describes that a rib of a connection bone portion (pattern block) formed by the rib and a lug is attached to a mold body (sector) by using an attachment bolt. However, with this attachment method, since a bottom surface of the pattern block is merely placed on the sector, there is a problem of not being capable of strengthening rigidity of the pattern block in addition to a problem of positional accuracy. Accordingly, in order to secure the strength, there is no other choice but to weld and fix the pattern block along an outer shape thereof, and thus man-hour is unavoidably increased.
In Patent Literature 3, a fixing portion formed at both ends of each piece (pattern block) is fitted into a fitting groove of a block (sector) to thereby attach each piece to the block in a fitted manner. With this configuration, fixing is not performed using fastening means, unlike conventional techniques.
However, this method involves a complicated processing of forming the fitting groove of the block.